Lecture 2 - Digestion and Absorption Flashcards
Digestion
the process by which foodstuffs are broken down by the GIT into absorbable units
4 types of digestion processes
- mechanical
- chemical
- enzymatic
- microbial
Mechanical digestion
- mastication (chewing)
- grinding of gizzard (birds)
- movement of GIT (segmentation and peristalsis)
Chemical digestion
- gastric acid (HCl; pH = 1.5-3.5)
Absorption
the process of moving digested products through the gut mucosal wall (transcellular or paracellular)
3 types of absorption transport mechanisms
- passive transport (transcellular or paracellular
- osmosis
- active transport (primary and secondary)
What is the amount of water secreted dependent on?
- diet; carnivore vs herbivore
What is the location of water absorption dependent on?
- the species
In what form are carbohydrates transported across cell membranes
MONOSACCHARIDES
- glucose
- fructose
- galactose
What are the 3 disaccharides?
- sucrose = gluctose + fructose
- maltose = gluctose + gluctose
- lactose = gluctose + galactose
What are 2 polysaccharides consumed in a diet?
- starch
- cellulose
Dextrins
mixtures of polymers of glucose units linked by alpha-1,4 or alpha-1,6 glycosidic bonds
What polysaccharide can amylase not digest? Why?
- cellulose
- cannot digest the beta-1,4 glycosidic bond but microbes can
What are the steps of CHO digestion?
- Mouth: starch, lactose, sucrose, and cellulose enter; alpha-amylase in mouth from saliva; end up with starch dextrins, isomaltose, maltose, lactose, sucrose, and cellulose
- Stomach: low pH stops action of amylase
- Pancreas: action of pancreatic alpha-amylase = isomaltose, maltose, lactose, sucrose, and dextrins
- Mucosal cell membrane-bound enzymes (oligoglucosidase, maltase, lactase, sucrase): end up with glucose, fructose, and galactose which enter the portal circulation and are taken to the liver
During what 2 points of CHO digestion is alpha amylase secreted?
- saliva
- pancreas
How are monosaccharides absorbed?
- secondary active transport
- 3 transporters = SGLT1, GLUT5, GLUT2
What breaks down starch?
amylase (salivary and pancreatic)
4 structures of amino acids
- primary = aa chain
- secondary = folding; hydrogen bonding of peptide backbone
- tertiary = packing; side chain interactions forming 3D structure
- quaternary = interaction of more than 1 aa chain
What form are 90% of ingested fats in?
- triglycerides
Where are bile acids produced?
- produced by liver, stored by gallbladder to digest fat
Are bile acids fat soluble?
- no, they stay in the gut working until actively transported in the ileum
What is the mechanism of ‘attack’ for bile acids?
- bile salts coat fat droplets
- pancreatic lipase and colipase break down fats into monoglycerides and FA stored in micelles
3 a. monoglycerides and FAs move out of micelles and enter cells via diffusion
3 b. cholesterol is transported into cells by membrane transporter - absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons
- chylomicrons released into lymphatic system
What is a chylomicron composed of?
- triglyceride + cholesterol + protein
- formed in intestinal cells after fat absorption
Purines and pyrimidines
- purines: adenine, guanine
- pyrimidines: thymine, cytosine, uracil
Chromosome structure
- strands of DNA wrap around a protein (histone) forming nucleosomes
- nucleosomes coil together forming chromatin
- chromatin loops and coils together forming supercoils
- supercoils bunch together = CHROMOSOME
How are nucleic acids digested and absorbed?
- denatured by gastric acid
- broken down to nucleotides by pancreatic nucleases
- phosphatase on brush border cleaves phosphate ion
- nucleosidase catalyzes breaking of covalent bond btw nitrogenous base and pentose sugar
Where are nucleotide breakdown products absorbed?
- duodenum and jejunum via active and secondary active transport
